Interpretive Summary: The product AquaFrin™ was evaluated in the laboratory for antibacterial activity against bacteria that cause common diseases in farmed catfish. In addition, AquaFrin was evaluated for selective toxicity towards the type of blue-green algae which causes musty off-flavor in pond-raised channel catfish in the southeastern United States. AquaFrin was very toxic towards the bacteria that cause the two most common bacterial diseases in farmed catfish. AquaFrin was also toxic towards a type of musty-odor producing blue-green alga, but it was not very selective.

Technical Abstract:
Producers of pond-raised channel catfish in the southeastern United States can experience huge economic losses due to the bacterial diseases enteric septicemia of catfish (ESC) and columnaris and to the presence of the certain odor-producing cyanobacteria in production ponds that result in “off-flavor” catfish. AquaFrin™ (lauryl methyl pyrifrin), a product being evaluated for commercial use, is a member of a class of porphyrins shown to be very effective as antibacterial agents. As a preliminary step to assess the potential use of AquaFrin as a therapeutant against ESC and columnaris, we used a rapid bioassay to evaluate AquaFrin for antibacterial activity against the Gram-negative bacteria Edwardsiella ictaluri and two genotypes of Flavobacterium columnare (the etiological agents of ESC and columnaris, respectively) and the representative Gram-positive bacteria Staphylococcus aureus (ATCC 29213) for comparison. In addition, we performed a bioassay-directed evaluation of AquaFrin for selective toxicity toward the musty cyanobacterium Planktothrix perornata. AquaFrin was found to possess antibacterial activity towards all bacteria tested. AquaFrin had stronger activity against F. columnare ALM-00-173, F. columnare BioMed, and S. aureus [minimal inhibitory concentration (MIC) of 0.6, 1.0, and 0.1 mg/L, respectively] compared to E. ictaluri (MIC of 9.8 mg/L). The range of 96-h 50% inhibition concentration (IC50) results (0.07-0.2 mg/L) for AquaFrin toward P. perornata and the green alga Selenastrum capricornutum indicates strong potential for its use as a broad-spectrum algicide.